The present invention relates generally to a hydraulic shock absorber for absorbing shock applied thereto and is applicable to a vehicle suspension, for example. More particularly, the invention relates to an improvement for a vortex shock absorber having a variable absorbing force which depends not only on the piston speed but also on the piston stroke, and to a simple construction for assemblying such a shock absorber.
Vortex shock absorbers have been well-known as applied to vehicle suspensions, for example. In such a shock absorber, a piston slidably received within a cylinder is provided with a vortex chamber therein. The piston defines upper and lower chambers within the cylinder. The vortex chamber is communicated with the upper and lower chambers via a vortex passage tangentially opening thereinto so that the fluid flow introduced therein generates a vortex for producing the absorbing force. Conventionally, the absorbing force produced by the shock absorber varies depending on the piston speed in response to the shock.
In case of the shock absorber applied to the suspension of an automotive vehicle, it is preferable to provide a relatively small absorbing force against a relatively small piston stroke, even though piston speed is relatively high, for riding comfort. On the other hand, for a relatively large piston stroke, a relatively large absorbing force is required for vehicle stability. Therefore, a shock absorber for use with an automotive vehicle suspension is required to vary the absorbing force against shock depending not only on piston speed but also on piston stroke.
In general, the piston stroke corresponding to various vehicle driving conditions are approximated as follows:
______________________________________ abrupt turning 40 mm rapid acceleration 50 mm lane change 35 mm crossing bump 3 mm smooth road 2 mm rough road 14 mm ______________________________________
As explained above, when the vehicle is turned abruptly, rapidly accelerated, or changes lanes, a significant absorbing force is required for adequate driving stability. On the other hand, when the vehicle is driven over a slight bump, on a smooth road, or on a relatively rough road, a significant absorbing force is not required since the vehicle is easily maintained in a stable condition. In the latter driving condition, it is important to provide minimal absorbing force for riding comfort.
Meanwhile, for communication between the upper and lower fluid chambers, defined opposite the upper and lower sides of the piston, and the vortex chamber, the piston is formed with one or more vortex passages. Generally, the vortex passage comprises vertical and horizontal sections formed in the periphery of the piston. To provide for the vortex passages, the periphery of the piston must be sufficiently thick. This places a lower limit on the volume of the piston and in turn on the volume of the shock absorber.
Furthermore, in the conventional shock absorber, since the vertical and horizontal sections of the vortex passages are formed integrally in the periphery of the piston, the vortex passages make machining of the piston more difficult.